Precision machine vision inspection systems (or “vision systems” for short) can be utilized to obtain precise dimensional measurements of inspected objects and to inspect various other object characteristics. Such systems may include a computer, a camera and optical system, and a precision stage that is movable in multiple directions so as to allow the camera to scan the features of a workpiece that is being inspected. One exemplary prior art system that is commercially available is the QUICK VISION® series of PC-based vision systems and QVPAK® software available from Mitutoyo America Corporation (MAC), located in Aurora, Ill. The features and operation of the QUICK VISION® series of vision systems and the QVPAK® software are generally described, for example, in the QVPAK 3D CNC Vision Measuring Machine User's Guide, published January 2003, and the QVPAK 3D CNC Vision Measuring Machine Operation Guide, published September 1996, each of which is hereby incorporated by reference in their entirety. This product, as exemplified by the QV-302 Pro model, for example, is able to use a microscope-type optical system to provide images of a workpiece at various magnifications, and move the stage as necessary to traverse the workpiece surface beyond the limits of any single video image.
In such vision systems, a light source having a controllable illumination direction may enhance the observation and inspection of workpieces. Controllable light sources may project light onto the workpiece at an adjustable angle of incidence relative to an axis which is normal to the imaging plane, to image textured surfaces or edges with improved contrast, for example. Controllable light sources may also adjust the nominal azimuthal angle of lighting direction about the axis normal to imaging plane. Typically, the nominal azimuthal angle is adjustable or selectable using addressable sectors, such as quadrants or octants of the light source. Additionally, the intensity of the light source can be controlled.
Some controllable light sources are configured as multiple LEDs arranged in concentric annular circular or rectangular patterns, and may be subdivided into quadrants or controllable blocks. The LEDs may direct their light through a Fresnel or conventional lens to provide a desired angle of incidence. Some controllable light sources have fiber optic or other conventional sources that are arranged in quadrants or the like, and that are directed to roughly hemispherically-shaped reflectors that are mechanically adjusted to provide a desired angle of incidence. Examples of various known types of controllable light sources are included in U.S. Pat. Nos. 4,706,168; 6,179,439; 5,690,417; and 5,897,195, each of which is hereby incorporated by reference in its entirety. However, known controllable light sources have various shortcomings. For example, lights sources which use mechanical adjustments typically have a slow adjustment response time that may limit the throughput of a vision system configured to acquire dozens of images without stopping the motion of the vision system at each feature, but rather by freezing each image using strobe illumination. In contrast, known controllable lights sources which change the angle of incidence by addressing LED's have a fast response time, but have a relatively large size in order to accommodate the number of LEDs that provide the desired number of illumination directions and the desired illumination intensity. Such devices typically extend in various directions beyond the objective lens of the vision system, interfering with the positioning of some workpieces. The spacing between the individual LED sources and the field of view is also typically relatively large (tens of millimeters) in such devices. Thus, the 1/r^2 drop in illumination intensity from the source limits the illumination intensity at the field of view, which extends the required exposure time for an image, limiting the throughput of a vision system that uses strobe illumination, for example. An improved controllable light source that overcomes these and other disadvantages, either individually or in combination, would be desirable.